test: remove unreachable code in pytest.raises block, fix some malformed tests

[bearomorphism]

Why

with pytest.raises block should contain only one statement which we expect it to throw exceptions.

Changes made

• Removed unreachable code in tests
• Fixed test_check_command_cli_overrides_config_message_length_limit. The last check_cmd assignment had no effect.
• Extracted success_mock

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.95%. Comparing base (52d84c1) to head (fcbfb0a).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1800   +/-   ##
=======================================
  Coverage   97.95%   97.95%           
=======================================
  Files          60       60           
  Lines        2646     2646           
=======================================
  Hits         2592     2592           
  Misses         54       54           

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